1. Field of the Invention
The present invention relates generally to fastening devices, and more particularly to a fastening device for fastening a heat sink to an electronic device to dissipate heat generated by the electronic device.
2. Description of Related Art
It is well known that, during operation of a computer, electronic devices such as central processing units (CPUs) frequently generate large amounts of heat. The heat must be quickly removed from the electronic device to prevent it from becoming unstable or being damaged. Typically, a heat sink is attached to an outer surface of the electronic device to absorb heat from the electronic device. In order to keep the heat sink to in close contact with the electronic device, a fastening device is desired.
A conventional fastening device for heat sink comprises a shaft having threads machined onto an exterior thereof and a slot defined around the shaft above the threads. A helical spring surrounds the shaft. A retaining collar tightly engages with the slot of the shaft. When it is assembled with a heat sink, the shaft of the fastening device is inserted into a through hole defined in the heat sink. The threads of the shaft pass through and are positioned under the through hole. The helical spring is located above the through hole. The shaft is pressed so that the slot of the shaft extends beyond the through hole of the heat sink. The retaining collar then holds the shaft in the slot. Here, the helical spring is deformed somewhat. Therefore, the fastening device is attached to the heat sink. When the heat sink preassembled with the fastening device is secured to an electronic device mounted on a printed circuit board, the threads of the shaft of the fastening device extend beyond a through hole defined in the printed circuit board and engage with a back plate located under the printed circuit board. The helical spring of the fastening device is deformed further and presses the heat sink to intimately contact the electronic device. However, the retaining collar is generally small, and it needs to be splayed to hold the shaft at the slot. Furthermore, it needs to press the shaft of the fastening device and overcome spring force from the helical spring to push the slot of the shaft beyond the through hole of the heat sink. This can make it difficult to assemble the fastening device with the heat sink.
What is needed, therefore, is a fastening device for a heat sink which can be conveniently assembled with the heat sink.